Method and apparatus for generating digital halftone images by multi color dithering

Abstract

The invention provides a method and apparatus for the reproduction of color images by multi-color dithering. Multi-color dithering is an extension of bi-level dithering for halftoning an input image using as primary colors an arbitrary number of inks. The inks may comprise standard inks or non-standard inks such as non-process color inks, opaque inks, metallic inks, variable color inks and fluorescent inks. Multi-color dithering provides a solution for creating artistic multi-color dithered images, whose screen elements are made of artistic color screen shapes such as micro-letters, symbols and ornaments. When printed at high resolution and at high registration accuracy, multi-color dithering using large dither arrays incorporating artistic dither shapes provides an effective solution for preventing counterfeiting. The use of non-standard inks offers additional protection. Multi-color dithering also offers a solution for printers requiring that all inks are printed side by side, without overlaps.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates generally to the field of digital image synthesis and, more particularly to digital color image reproduction, digital color image printing, digital color image display and anti-counterfeiting protection. The invented method and apparatus enable generating digital halftone images by multi-color dithering. The invented method and apparatus are particularly effective for generating images on color printers printing with more colors than cyan, magenta, yellow and black, and for generating images incorporating microstucture patterns (micro-characters, symbols and ornaments) made of a combination of standard and non-standard inks. Non-standard inks comprise non-process colors, opaque inks, and special inks such as metallic ink, variable color inks and fluorescent inks. The generated images are displayed on color displays or printed on physical output devices such as ink-jet printers, electrophotographic printers, offset printe...

AI Technical Summary

Benefits of technology

[0011]The present invention provides a method and apparatus and a preferred implementation as a computing system for the reproduction of color images by a new method that will be called hereinafter “multi-color dithering”. Multi-color dithering is characterized by the use of a two-dimensional dither function and the use of an arbitrary number of inks and superposition of inks as primary colors. The inks may comprise standard inks and non-standard inks such as non-process colors, opaque inks, metallic inks and variable color inks. Multi-color dithering provides a solution for printing color images with a freely chosen set of standard or non-standard inks. It also provides a solution for creating artistic multi-color dithered images incorporating a microstructure made of artistic color screen shapes such as micro-letters, symbols and ornaments. When printed at high resolution and at high registration accuracy, multi-color dithering using large dither arrays incorporating artistic dither shapes provides an effective solution for preventing counterfeiting. The use of non-standard inks offers additional protection. Multi-color dithering offers also a solution for printers requiring that all inks are printed side by side, without overlaps.

Problems solved by technology

When prepared at a high resolution of R dots per inch (dpi), for example 1200, 2540 or 4000 dpi and printed at a resolution Rp>=R, these multi-color dithered images are extremely difficult to reproduce by potential counterfeiters.

An attempt to photocopy such a multi-color dithered image with a photocopying device of resolution lower than R results in a heavy degradation or a loss of the artistic shape (micro-letters, symbols, ornaments) and in the loss of the original non-standard ink primary colors.

Printing a multi-color dithered image with non-standard opaque inks at a high registration accuracy, for example at a registration accuracy ua>=1 / (2R) inch, makes counterfeiting extremly difficult to achieve.

Images